In a rotary throttle valve carburetor, fuel flows into the throttle passage of a rotary throttle valve through a nozzle tube, which is supported on the carburetor body at one end of the rotary throttle valve.
Generally, the rotary throttle valve carburetor is provided with a diaphragm device in between a fuel pump and the nozzle tube for supplying a prescribed amount of fuel to the nozzle tube regardless of the carburetor position.
However, in the prior art, with this type of carburetor, the diaphragm device is incorporated into the carburetor body in a position outwardly of the circumference of the rotary throttle valve. Therefore, the fuel passage leading to the nozzle tube from the constant pressure chamber in the diaphragm device is comparatively long in length. The reason for this is that the passage is extended from the constant pressure chamber around the end of the carburetor body to the nozzle tube which is located parallel with the circumference and in the direction of the axis of the rotary throttle valve. The passage is then joined at a 90.degree. angle to the nozzle tube.
For the purpose of promoting efficient engine response, and coordinating with the throttle valve opening, it is advantageous to locate the fuel guide passage directly between the nozzle tube and the constant pressure chamber.
Further, it is desirous that atomized fuel vapor or an air and fuel mixture in the constant pressure chamber be quickly discharged from the throttle chamber through the fuel passage. In the prior art, the design is such that there is a possibility of the fuel vapor being trapped in the angle of the fuel passage. This trapped vapor interferes with the operating efficiency of the engine since the vapor prevents the prescribed amount of fuel flow from reaching the engine.
Accordingly, it is an object of this invention to design a rotary throttle valve carburetor that can achieve engine response according to the throttle valve setting as well as improve the efficiency of the engine.
A feature of this invention is to promote engine efficiency and response by locating the diaphragm device with the constant pressure chamber at the exterior of the carburetor body adjacent the end of the rotary throttle valve where the nozzle tube passes into the throttle passage. This results in the fuel passage from the constant pressure chamber to the nozzle tube being essentially straight and also shortens the length of the passage.
Additional features of this invention will be apparent in the following description and claims taken in connection with the accompanying figure illustrating, by way of example, a preferred embodiment of this invention.